The present invention relates in general to a droplet ejection apparatus that ejects droplets on an ejection target medium which is conveyed on a platen, and relates in particular to a droplet ejection apparatus capable of calculating a distance between a head for ejecting droplets and the platen or the ejection target medium.
There has been devised a technique in which a distance between an ejection target medium which is conveyed on a platen and a head for ejecting droplets is calculated and used for a variety of control. In a proposed example, a printing head for ejecting ink on a printing sheet as an ejection target medium is mounted on a carriage, and a sensor, including a light emitting portion, a first regular reflection light receiving portion and a second regular reflection light receiving portion, is also mounted on the carriage.
The first regular reflection light receiving portion is disposed at a position such that when a light emitted from the light emitting portion is reflected by a thick glossy paper as a printing sheet, the first regular reflection light receiving portion receives a regular reflection light.
The second regular reflection light receiving portion is disposed at a position such that when a light emitted from the light emitting portion is reflected by a thin glossy paper as a printing sheet, the second regular reflection light receiving portion receives a regular reflection light. Accordingly, calculation of a distance between the printing sheet and the head can be performed by comparing a light receiving amount of the first regular reflection light receiving portion and a light receiving amount of the second regular reflection light receiving portion.
The above described configuration, however, requires a plurality of light receiving portions to be provided. This leads to an increase in manufacturing cost and inefficiency in assembly operation. Providing a plurality of light receiving portions also leads to an increase in size of the carriage, which does not comply with a requirement to downsize an entire droplet ejection apparatus. Furthermore, since the positional relationship between the light emitting portion and the first regular reflection light receiving portion or the second regular reflection light receiving portion is fixed, accurate calculation of the above-mentioned distance is unlikely to be performed when a printing sheet to be used has an intermediate thickness between the thickness of the thick glossy paper and the thickness of the thin glossy paper.
Providing an increased number of reflection light receiving portions will allow more accurate calculation of the above-mentioned distance even in the case of using a printing sheet having an intermediate thickness. This, however, will lead to a further increase in manufacturing cost.
These days, there is a demand for calculating not only the distance between the head and the ejection target medium, but also the distance between the head and the platen. This results from the facts that the distance between the platen and the head actually varies in individual products and that the height of the platen is adjustable in a recently proposed model.